92 SOIL CONDITIONS AND PLANT GROWTH 



The nature of the compound is also important. Lohnis and Pillai 

 (i88) found that the following amounts of nitrogen were fixed per gram 

 of compound decomposed : — 



Little is known of the chemistry of the change, even the fate of the 

 sugar has not been definitely ascertained. The only obvious product 

 is carbon dioxide, fatty acids being formed only in small quantities, in 

 sharp contrast with Clostridium. 



Starting with IS"9 grams of dextrose Stoklasa (276) recovered 7-9 

 as carbon dioxide, 0'3 as ethyl alcohol, 0*2 as formic acid, 07 as acetic 

 acid, 02 as lactic acid, but could not trace the remaining 6 -5 grams. 



The nitrogen is found partly in compounds dissolved in the liquid, 

 but mostly in the bacterial mass. The organism is remarkably active, 

 one gram weight evolving no less than i -3 grams of CO3 in twenty-four 

 hours (273). An adequate supply of phosphate, calcium carbonate and 

 other mineral nutrients is essential, any deficiency limiting the amount 

 of fixation. Traces of nitrogen compounds are helpful in the early 

 stages, but larger quantities reduce the amount of fixation, and may 

 themselves suffer some change : thus sodium nitrate is partially re- 

 duced to nitrite and ammonia. Several forms of azotobacter are 

 now known : A. agilis, A. vinelandii, etc., and also various less 

 efficient nitrogen fixers that more resemble Clostridium, such as amylo- 

 bacter (53) and granulobacter, some of which are aerobic and others 

 anaerobic, but all form spores.^ The great distinction between the two 

 groups is that the azotobacter give carbon dioxide as the chief product 

 from the sugar, while the others, even the aerobic organisms, form 

 butyric acid in considerable amount and fix smaller quantities of nitrogen. 

 Amylobacter also makes and stores glycogen, a property possessed by 

 few other micro-organisms. 



Kossowitsch (154) has shown that a mixture of azotobacter and 

 algae, especially nostoc, can work together very well, the algae fur- 

 nishing the necessary carbon compounds, while the azotobacter fixes 



' A list is given by C. B. Lipman in yourn. Biol. Chem., 191 r, x., 169-82. 



